81633618 has 72 divisors (see below), whose sum is σ = 199865484. Its totient is φ = 24045120.

The previous prime is 81633611. The next prime is 81633619.

81633618 is a `hidden beast` number, since 8 + 1 + 6 + 33 + 618 = 666.

81633618 is nontrivially palindromic in base 10.

It can be written as a sum of positive squares in 2 ways, for example, as 79977249 + 1656369 = 8943^2 + 1287^2 .

It is not an unprimeable number, because it can be changed into a prime (81633611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 80080 + ... + 81092.

Almost surely, 2^81633618 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81633618, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99932742).

81633618 is an abundant number, since it is smaller than the sum of its proper divisors (118231866).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81633618 is a wasteful number, since it uses less digits than its factorization.

81633618 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1080 (or 1066 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 81633618 is about 9035.1324284705. The cubic root of 81633618 is about 433.8001337850.

It can be divided in two parts, 8163 and 3618, that added together give a triangular number (11781 = T₁₅₃).

The spelling of 81633618 in words is "eighty-one million, six hundred thirty-three thousand, six hundred eighteen".